Large modular PM generators

Wind-turbine installations are increasing in size as economic and other factors stimulate their proliferation. To use a generator of conventional shape and parameters requires a gearbox of increasing size and ratio. The advantages of any arrangement which eliminates the gearbox are mostly obvious-the main disadvantage is an increase in the size of any electrical generator which is directly coupled to the turbine. In spite of this, the design of generator described in this paper is proving to be a viable proposition. A significant factor in cost and weight is the diameter at the air gap-the larger this is, the better utilised will be the active materials of the machine. A relatively small pole-pitch permits generation at near normal frequency, and the use of permanent-magnet excitation allows a small pole-pitch to be used without the usual penalties associated with poor coupling such as poor power factor. Both of these features have been adopted, together with a modular form of construction, in the machine described. The major aspects of the construction are: magnets in a ´buried´ configuration with flux concentrators attached to magnet blocks to form a rotor module; stator magnetic material in the form of ´E´-cores with open slots, and in each of which is contained a single coil; and each ´E´-core attached to a support beam to form an isolated stator module. The main advantages of the construction are listed and discussed